When manufacturing powdery or granular detergents and cleaners to be used for large scale production type spray drying processes, the process starts with an aqueous slurry which incorporates most or even all of the detergent constituents. For economic reasons, it is important that the slurry be rich in detergent materials, but poor in liquid ballast materials. Therefore, the least possible amount of water for a slurry make-up is used. However, there are limitations with respect to maximum concentration that can be employed so as not to exceed the highest possible viscosity at which a slurry is still workable, i.e., at which the slurry can still be pumped and sprayed.
The main constituents of detergents and cleaner solutions are surfactants. The anionic surfactants for the manufacture of detergent slurries are usually in form of a paste concentrate with a surfactant content of about 30 to 60 wt. %. A higher surfactant content would be desirable but poses a problem with respect to the workability of concentrated surfactants having high viscosity. A characteristic rheological property of concentrated surfactants is that when adding water to the concentrate the viscosity does not decrease at first but will actually thicken and form a glutinous mass creating problems for the manufacturer. For example, it is not always easy to redissolve the glutinous mass; or unclog the valves on pumps and containers.
In order to try to solve these problems, several approaches have been tried. German Published patent application DE No. 22 51 405 A1 describes the use of salts of certain carboxylic acids, in particular, hydroxy-carboxylic acids, as viscosity modifiers. German Published patent application DE No. 23 05 554 A1 discloses that sulfonated aromatic compounds can be used for this purpose. German Published patent application DE No. 23 26 006 A1 describes sulfates or sulfonates of aliphatic, as well as substituted hydrocarbons, as viscosity modifiers. Even the addition of lower alkanols is mentioned in the above publications as agents for modifying viscosity. Furthermore, the addition of known hydrotropes such as cumene sulfonate or acidic phosphoric acid esters (German Published patent application DE No. 16 17 160 A1) or multivalent alcohols of certain carboxylic acids and/or esters of these compounds (European Published application No. 8060 A1) are described. From European Published patent application No. 24 711 A1 it is known that in order to improve the fluidity of anionic surfactant concentrations, sulfates of certain polyalkylene-ether glycols can be added.
However, some additives that are disclosed in the literature will only work for certain surfactants, others dilute the concentrates too much with addtives not otherwise suitable as detergent additives, some are only effective when added in large amounts, and some others such as lower alkanols will lower the flash point to an unacceptable level.